OpenAI has published details of the Windows sandbox architecture powering its Codex coding agent. After finding existing Windows isolation mechanisms insufficient for autonomous coding agents, OpenAI built a custom approach using security identifiers (SIDs), access control lists (ACLs), and restricted tokens. An initial 'unelevated sandbox' used a synthetic sandbox-write SID to restrict writes to designated directories. A later 'elevated sandbox' redesign introduced dedicated local Windows accounts (CodexSandboxOffline and CodexSandboxOnline) with firewall-controlled network access. The design aims to let Codex operate on real developer environments without requiring constant approval or granting unrestricted system access.
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